Steel balls used in ball bearings, etc., are first made from wire materials into roughly spherical blanks having flashes. Then, they are subjected to flashing process to remove such flashes, heat treatment to impart the required strength and durability to the balls, grinding process thereafter, and lapping process to finish the balls with high accuracy after the grinding process.
FIG. 6 illustrates a steel ball machining apparatus 70 of the prior art, which used the above-mentioned flashing, grinding, and lapping processes. The apparatus 70 comprises a machining mechanism 76 having a rotary plate 72 and a stationary plate 74, and a rotor conveyor 80 having a cylindrical vessel 82 for supplying steel balls 78 between the rotary plate 72 and the stationary plate 74 and receiving the steel balls 78 therefrom.
The steel balls 78 supplied by the conveyor 80 are held between the rotary plate 72 and the stationary plate 74 and after moving through almost a complete circle between the rotary plate 72 and the stationary plate 74, the balls 78 are returned to the conveyor 80. The balls 78 circulate through the machining mechanism 76 and the conveyor 80 until the predetermined dimensional accuracy is attained tained.
The balls 78 discharged near the outer wall 84 of the vessel 82 tend to move along the outer wall 84 and the balls discharged near the inner wall 85 of the vessel 82 tend to move along the inner wall 85 before they are sent out to the machining mechanism. Consequently, it takes a long time to achieve the desired value of the lot diameter vairation (see JIS B 1501), which is one of the most important quality criteria of steel balls for ball bearings.
As the demand for higher quality is increasing these days, it has been necessary, in order to achieve said desired value of the size variation, for an operator to agitate the steel balls contained within the cylindrical vessel. Thus, the object of the present invention is to provide a steel ball machining apparatus which is capable of efficiently mixing steel balls circulating through the cylindrical vessel and the machining mechanism, thereby minimizing the size variation of the processed steel balls.